In an electrophotographic image forming apparatus, when the total number of printed sheets (i.e., total number of sheets printed with one toner cartridge) becomes large, the charge amount of developer decreases greatly due to degradation of the developer. As a result, the density of the developer increases. In order to suppress the increase in the density of the developer, a known technique suggests that the developing bias is lowered when the total number of sheets printed by the image forming apparatus is equal to or greater than a predetermined value. To be more specific, for example, the total number of printed sheets is counted as developer consumption, and the developing bias is lowered when the developer consumption is equal to or greater than a predetermined value.